Method of preparing a fluoropolymer composite

ABSTRACT

Described herein is a method of preparing a fluoropolymer composite tube comprising the steps of activating a formed fluoropolymer substrate by subjecting the substrate to a charged gaseous atmosphere formed by electrically ionizing a gas which contacts the substrate and thereafter applying a layer of a thermoplastic polymer to the activated fluoropolymer substrate. The ionizing step can be described as a corona discharge or an electrically formed plasma. In particular, described is a fuel pipe comprised of an inner fluorocarbon layer having electrostatic discharge resistance and hydrocarbon evaporative emission resistance and on top of and integral with, the fluorocarbon layer an outer layer of a thermoplastic polymer. Fluoropolymer layers have excellent chemical resistance.

This is a continuation of application Ser. No. 08/200,941 filed on Feb.23, 1994, abandoned, which is a continuation of Ser. No. 07/817,304filed Jan. 6, 1992, abandoned.

TECHNICAL FIELD

The invention pertains to the field of fluoropolymer tubes such asfluoropolymer composite pipes such as those used in fuel lines.

BACKGROUND ART

With the advent of increased concern with evaporative fuel standards,there has been an increasing need for fuel lines that have increasedevaporative emission requirements while at the same time, having highelectrostatic discharge resistance. Further, any fuel line must likewisehave economic concerns that it be amenable to high production at a lowcost. A desired fuel line likewise should have appropriate physicalproperties of sufficient tensile strength and kink resistance, that is,the resistance of the fuel line to retaining a particular shape uponbending.

Fuel line hoses of a variety of materials have been suggested over theyears. Tetrafluoroethylene has been utilized and has excellent andoutstanding high temperature and chemical resistance. "Hose Technology",Publisher: Applied Science Publisher, Ltd., Essex England, by: Colin W.Evans, pages 195 through and including page 211. Nylon has also beenutilized as a hose composition. The difficulties with many who haveattempted to utilize fluorinated polymers is the difficulty of suchmaterials to adhere to or have adhered to them other materials to makedesirable composites.

U.S. Pat. No. 4,933,060 discloses surface modification of fluoropolymersby reactive gas plasma. The reference, however, further indicates thatin order to have sufficient bonding that adhesives must be utilizedprior to the application of an additional layer. Suitable adhesives areepoxys, acrylates, urethanes, and the like.

U.S. Pat. No. 4,898,638 teaches a method of manufacturing flexiblegaskets which withstand chemical agents. Flexible gaskets are preparedwhere one film of PTFE (polytetrafluoroethylene) is directly appliedonto a sheet of raw rubber and subjecting the sheet of rubber togetherwith the film of PTFE to heating and to pressure suitable for causingthe rubber to vulcanize. Use of adhesives in the bonding offluoropolymers is likewise described in U.S. Pat. No. 4,743,327 andtheir use is required to make the development operative. Activatingfluoropolymers utilizing ammonia gas is taught in U.S. Pat. No.4,731,156.

None of the prior art describes a multi-layered fluoropolymer with alayer of a nylon that is integral with the fluoropolymer which combinedmulti-layered composite or pipe has desirable electrostatic dischargeresistance and hydrocarbon evaporative emission resistance. Further, theprior art suggests the need for adhesives to firmly and fixedly joinplastic layers. This invention does not have as an essential requirementthat additional adhesives are needed in joining the fluoropolymer layerto the thermoplastic layer.

It is an object of the present invention to have a fuel pipe or tubethat has a fluoropolymer substrate that is activated sufficiently to beable to have an integral top coat or layer of a thermoplastic polymersuch as nylon.

It is also an object of the present invention to prepare a fluoropolymercomposite by extruding a multi-layered fluoropolymer substrate, onelayer of which has desirable electrostatic discharge resistance and ontop of the fluoropolymer layers would be an extruded plastic layer suchas a polyamide, preferably nylon.

SUMMARY OF THE INVENTION

The present invention is concerned with a method of preparing afluoropolymer composite tube comprising the steps of:

(1) activating a formed fluoropolymer substrate by subjecting thesubstrate to a charged gaseous atmosphere formed by electricallyionizing a gas which contacts the substrate;

(2) and thereafter applying a layer of a thermoplastic polymer to theactivated fluoropolymer.

The invention is also concerned with a fuel pipe comprised of an innerfluorocarbon layer having electrostatic discharge resistance andhydrocarbon evaporative emission resistance, and on top of and integralwith the fluorocarbon layer, an outer layer of a thermoplastic polymer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view of the three-layered fuel pipe of thepresent invention;

FIG. 2 is a cross-sectional view of FIG. 1 along lines 2--2;

FIG. 3 is a schematic diagram of the process for the method of preparingthe fuel pipe of the present invention;

FIG. 4 is a cross-sectional view of the multi-inlet extrusion die usedin the method of preparing the fuel pipe of the present invention;

FIG. 5 is a cross-sectional taken along the lines 5--5 of FIG. 4;

FIG. 6 is a cross-sectional view of the interior of the multi-inletextrusion die taken along the lines 6--6 of FIG. 7;

FIG. 7 is a cross-sectional view taken along the lines of 7--7 of FIG.6;

FIG. 8 is a cross-sectional view taken along the lines 8--8 of FIG. 6;

FIG. 9 is a cross-sectional view taken along the lines 9--9 of FIG. 6;

FIG. 10 is a cross-sectional view taken along the lines 10--10 of FIG.6;

FIG. 11 is a cross-sectional view of the center extrusion die that is apart of the multi-inlet extrusion die of FIG. 4;

FIG. 12 is a cross-sectional view taken along the lines 12--12 of FIG.11;

FIG. 13 is a cross-sectional view taken along the lines 13--13 of FIG.11;

FIG. 14 is a cross-sectional view taken along the lines 14--14 of FIG.11;

FIG. 15 is a cross-sectional view taken along the lines 15--15 of FIG.11;

FIG. 16 is a cross-sectional view of the outer extrusion die which is aportion of the coextrusion multi-inlet die of FIG. 4;

FIG. 17 is a cross-sectional view taken along the lines 17--17 of FIG.16;

FIG. 18 is a cross-sectional view taken along the lines 18--18 of FIG.16;

FIG. 19 is a cross-sectional view taken along the lines 19--19 of FIG.16;

FIG. 20 is cross-sectional view taken along the lines 20--20 of FIG. 16;and

FIG. 21 is a cross-sectional view of the cross-head die as schematicallyshown in FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is concerned with a method of preparing afluoropolymer composite such as a pipe or tube. In particular, it ispreferred that the fluoropolymer be a multi-layered fluoropolymer. It ispreferred that the fluoropolymer layer have electrostatic dischargeresistance as well as hydrocarbon evaporative emission resistance. Theelectrostatic discharge resistance is obtained preferably by making thefluoropolymer layer a conductive fluoropolymer. In this fashion, theelectrostatic charge (electricity) that maybe generated during the flowof fuel or other fluids through the pipe or tube can be carried toground.

It is also to be appreciated that the composite tube may have multiplelayers without the presence of a conductive filler. Due to the need ofhaving on board a vehicle a refueling vapor recovery system, it may bedesirable to have a layer (or layers) of fluorocarbon polymer surroundedby a thermoplastic polymer. In this manner, the fuel vapor alone cantravel through the fluoropolymer/thermoplastic polymer composite tube toany desirable location in the vehicle, e.g. an on board carbonaceouscontaining canister. The carbon material can absorb the fuel vapors.

The fluoropolymers that may be utilized are any of the availablefluoropolymers, many of which are commercially available. Suitablefluoropolymers are ethylene-tetrafluoroethylene (ETFE),ethylene-chlorotrifluoroethylene (ECTFE), fluorinated ethylenepropylene(FEP), perfluoroalkoxy (PFA), polyvinylfluoride (PVF), polyvinylidenefluoride (PVDF), polychlorotrifluoroethylene (PCTFE),polytetrafluoroethylene (PTFE). Other fluoropolymers are those that areprepared from perfluorinated α-fluoroolefin monomers containing hydrogenatoms as well as fluorine atoms. The α-fluoroolefin has 2-6 carbonatoms. Typical α-fluoroolefins may be perfluorinated α-fluoroolefinssuch as hexafluoropropene, perfluorobutene, perfluoroisobutene, and thelike, and hydrogen containing α-fluoroolefins such as trifluoroethylene,vinylidene fluoride, vinyl fluoride, pentafluoropropane, and the like,and halogen-containing α-fluoroolefins such as trifluorochloroethylene,1, 1-difluoro-2,2 dichloroethylene, 1, 2-difluoro-1, 2 dichloroethylene,trifluorobromoethylene and the like, and perfluoroalkoxyethylenepolymers. The most preferred fluoropolymer is ETFE sold under thetrademark Tefzel® (trademark of DuPont).

The layer of fluoropolymer that is to be conductive in order to carryaway the electrostatic discharge can generally be made conductive in awell known manner. This conductivity can occur by adding conductiveparticles to the fluoropolymer resin prior to processing. Theelectrically conductive particles incorporated into fluoropolymers aredescribed in U.S. Pat. No. 3,473,087, hereby incorporated by reference.Suitable conducting materials would be carbon black in the amount of0.1-10 weight percent of the total fluoropolymer layer, preferably 0.1-2weight percent. The carbon black is blended with the fluoropolymer priorto the extrusion taking place. Conductive fluoropolymer resin islikewise commercially available.

It is preferred that the fluorinated polymer be extruded by a meltextrusion technique where the first layer would be a conductivefluoropolymer and coextruded with it would be the second layer on top ofthe first layer wherein the second layer is a fluoropolymer without theconducting particles therein.

On top of the second fluoropolymer layer, and integral with it is anextruded thermoplastic material. The thermoplastic material can be avariety of thermoplastic resinous materials. Suitable materials would bethose that can be melt extruded on top of the extruded fluoropolymerpipe or tube. Such resinous materials could be acrylate materials,polyester materials, bromoisobutene-isoprene materials, polybutadiene,chlorinated butyl rubber, chlorinated polyethylene,polychloromethyloxirane, chloroprene, chlorosulphonylpolyethylene,ethyleneoxide and chloromethyloxirane polymer.Ethylenepropylenedieneterpolymer, ethylenepropylenecopolymer,polyetherurethanes, isoprene, isobutene isoprene, nitrile butadiene,polyamide, polyvinylchloride, styrenebutadiene, polysulfide,polyolefins, polyphenylsulfides and polysulfones (e.g. Astrel, atrademark of 3M, polyether sulfone of ICI and Udel, a trademark of UnionCarbide). Most preferably, a polyamide is employed, and even morepreferably, a nylon such as nylon 66 which is a condensation product ofadipic acid and hexamethylenediamine, nylon 6 which is a polymer ofcaprolactam, nylon 4 which is a polymer of butyrolactam (2-pyrrolidone),nylon 2 made from butadiene, and the like. The most preferred nylon isthe nylon 12 available under the trademark of L25 FVS 40 from EMS ofSwitzerland.

In the melt extruding process for the formation of polyfluoropolymerlayers, the extrusion temperature that is utilized ranges from about500° to about 800° F., preferably about 550°-700° F., with the screwrevolutions per minute (RPM) ranging from about 1 to about 100 RPM,preferably 5-50 RPM.

The end product that is produced is the multi-layered fluoropolymerhaving a thermoplastic material on top 10 as shown in FIGS. 1 and 2. Theconductive layer 12 is co-extruded with the non-conductive layer 14. Theconductive particles (not shown) are present in the layer 12.

When the multiple layers of fluoropolymer composite without conductivefiller is desired, then the same fluoropolymer is co-extruded to formthe multiple layers. Obviously, one may desire only one fluoropolymerlayer, in which case, a single extrusion die could be used. Thereafter,the additional processing steps are followed.

Prior to the extruding of the top thermoplastic, e.g. polyamide layer10, the fluoropolymer should be activated. In other words, the outerportion of layer 14 which is to come into contact with the layer 10should have its surface activated by plasma discharge or coronadischarge. By this is meant that the fluoropolymer layer 14 is to besubjected to a charged gaseous atmosphere that is formed by electricallyionizing a gas which contacts the substrate 14. It is most preferredthat the corona electrode orientation be on opposite sides of the movingfluoropolymer tube. In other words, there is a first stage for coronaelectrode discharge where approximately 270° of the plastic tube issubjected to the corona discharge. The tube is anywhere from about 0.05to 3 inches, preferably 0.1 to 0.5 inches from the electrode as the tubepasses through the corona electrode discharge. Thereafter, withinapproximately 3 inches to 3 feet, preferably 6" to 18" from the firstcorona discharge device, the tube comes in contact with a second stagecorona discharge placed on the opposite side from the first side whereagain the tube is subjected to approximately a 270° contact around thetube with the corona discharge. In this fashion, the entirecircumference of 360° of the tube is subjected to activation by coronadischarge.

The corona discharge equipment that is most preferably employed isavailable from Enercon Dyne-A-Mite, Model B12, which uses an air blownelectrical arc to form the treatment plasma. In other words, there aretwo separate corona discharge heads making up two separate stages whichare in the open air, ambient temperature and pressure atmosphere. Eachcorona discharge head of the Enercon device, each trapezoidal in shape,has a pair of wire electrodes (0.065" diameter) in the same horizontalplane separated by a gap of 0.35" with an overall length from end of onewire electrode to end of the second wire electrode of 1.9".

It is to be appreciated that the open air and open atmosphere is themost preferred economical approach for corona discharge. It is to beappreciated further that depending upon the amount of activation that isrequired and the particular materials that are to be applied to thefluoropolymer that closed chamber electrode discharge devices could beutilized. In a closed chamber environment, a pair of oppositely charged(positive and negative electrodes) may be utilized by passing a currenttherebetween, thereby ionizing a gas. The substrate can pass through theelectric field which has ionized the gas. This gas may be altered bysupplying additional gases to the chamber such as oxygen, nitrogen,argon or other reactive gases such as carbon monoxide, fluorinatedgases, carbon dioxide, hydrogen fluoride, carbon tetrafluoride, ammonia,and the like. The chamber may be operated at vacuum pressure such asfrom 0.01 to 100 torr (1 atmosphere equals 760 torr).

A coextrusion die (FIG. 21) is used for high production rates.Therefore, the extruded tube as it passes through the corona dischargestage moves at a high constant rate. Preferably, the rate is from 1 footto fifty (50) linear feet per minute (FPM), preferably 15 to 30 FPM. TheEnercon device has treatment area for the corona discharge of about21/2" by 2" per head.

When the Enercon Dyne-A-Mite corona discharge device is utilized, theactivated tube is not significantly hot to the touch, but is perhaps 10°or 20° F. over ambient temperature. This increases the safety inmanufacturing the fuel tube or pipe.

After the activation of the fluorinated tube, the thermoplastic isextruded through the cross-head die as shown in FIG. 21 andschematically in FIG. 3. The cross-head die is at an extrusiontemperature sufficient to melt the thermoplastic resin. Generally, thetemperature is significantly less than the extrusion temperature of thefluorinated plastic. The operative temperature for the cross-head diewould range from about 300° to about 500° F., preferably 350° to about450° F. with a screw RPM of 10 to 100 RPM, preferably 20 to 60 RPM witha line speed of approximately 5 to 100 feet per minute, preferably 15 to70 feet per minute.

The Enercon device is preferably operated at an output of 15,000 voltswith 30 millamps plasma per electrode with 2 electrode stages beingemployed.

The wattage that is applied to the electrodes in order to ionize the gascan vary substantially. For example, the wattage may vary from 250joules/sec to 600 joules/sec when the tube being treated is about 25 sq.inches/min. (assuming 1" outer diameter OD tube 12" long), i.e. about 10to 24 joules per linear foot of tube.

Turning now to a description of the drawings, the schematic diagram ofFIG. 3 indicates that a coextrusion takes place in the coextrusion die20 from extruders 22 and 24. After the formed tube leaves die 20, itthen enters into die 26 which is in the entranceway to the vacuumwater-cooled chamber 28. The temperature of the water is roomtemperature. The tube is then passed along horizontally to the stretchpuller 30. The tube leaves the stretch puller and is exposed to thecorona discharge 32 schematically shown in FIG. 3. Thereafter, theactivated fluoropolymer substrate is subjected to an extrusion of athermoplastic polymer from extruder 34. The fluoropolymer inner layerpasses through crosshead die for sizing at reference numeral 36.Thereafter the composite tube is cooled by vacuum cooler 38. The tube ispulled axially through the vacuum cooler by puller 40 and thereafter iscut by cutter 42 to desired size.

The operation of the die will now be described. While FIG. 4 shows threeinlet lines, it is most preferred that a two inlet coextrusion die beutilized for two coextruded layers of fluorinated polymers to beprepared, one being the conductive layer and the other being anon-conductive layer. Obviously, if only a single layer of fluoropolymeris used, a commercially available tube forming extrusion die can beused.

The die assembly 50 shown in FIG. 4 includes a die housing 52 having aninner die member 56, a center die member 58 and an outer die member 60as the main structural members. The die members 56, 58 and 60 areconcentric and generally cylindrically-shaped extrusion die members.Throughbore 54 extends along axis "A" of the die assembly 50. The diemembers 56, 58 and 60 are held together by a bolt or pin 62 or the likewhich extends through the orifice 64.

With additional reference to FIG. 5, in the preferred embodiment, theextrusion die members 56, 58 and 60 have inlets 70, 72 and 74,respectively, extending inwardly from the outer periphery of the diehousing 50 to the associated die member. As best shown in FIG. 5, theinlet 70 preferably extends to a semi-circumferential distributionchannel 80, through which extrusion material is passed for distributionto the extrusion end 76 of the die assembly 50, as described in greaterdetail herein below.

As best shown in FIG. 10, the distribution channel 80 is in fluidcommunication with a pair of axial distribution channels 82. Asillustrated, the axial distribution channels 82 are preferably disposedsymmetrically around the inner die member 56 and extend therealongtoward the extrusion end 76.

Referring now to FIG. 6 and FIG. 9, there is shown cross-sections of theinner die member 56. Each axial distribution channel 82 is in fluidcommunication with a pair of branch distribution channels 84. Asillustrated, the branch distribution channels 84 extend around the innerdie member 56 in a generally semi-circumferential manner. The branchdistribution channels 84 are in fluid communication with four (4) axialdistribution channels 86.

With reference to FIG. 6, the axial distribution channels 86 extendalong axis "A" of the inner die member 56 toward the extrusion end 76.The channels 86 are in fluid communication with a plurality of branchdistribution channels 90, which extend around the inner die member 56 ina partial circumferential manner, as best shown in FIG. 8. In thepreferred embodiment, the distribution channels 90 are in fluidcommunication with eight (8) axial distribution channels 92 (only fourof which are specifically illustrated in FIG. 6), which also extendalong axis "A" toward the extrusion end 76. As shown in FIG. 6, theaxial distribution channels 92 are in fluid communication with aplurality of generally screw-shaped channels 94 disposed around theextrusion end 76 in a spiral manner.

Thus, extrusion material enters the inlet 70 and travels to the innerdie member 56. At semi-circumferential distribution channel 80, theextrusion material splits and enters the axial distribution channels 82.The material travels along the channels 82 and splits again at thebranch distribution channels 84. The extrusion material then enters theaxial distribution channels 86 and travels therealong to the branchdistribution channels 90, where the material splits again and enters theeight axial distribution channels 92. From the channels 92, theextrusion material enters the screw-shaped channels 94. Thesescrew-shaped channels 94 function to provide even distribution and gooduniformity of the extrusion material during the extrusion process.

Referring now to FIGS. 11 and 15, there are shown various cross-sectionsof the center die member 58. Extrusion material enters the center diemember 58 through the inlet 72 (as best shown in FIG. 1). The inlet 72preferably extends to a semi-circumferential distribution channel 100,through which extrusion material is passed for distribution to theextrusion end 76', as described in greater detail herein below.

As best shown in FIG. 15, the distribution channel 100 is in fluidcommunication with a pair of axial distribution channels 102. Asillustrated, the axial distribution channels 102 are preferably disposedsymmetrically around the center die member 58 and extend therealongtoward the extrusion end 76'. In the preferred embodiment, each axialdistribution channel 102 is in fluid communication with a branchdistribution channel 104. As best shown in FIG. 14, the branchdistribution channels 104 extend around the center die member 58 in agenerally semi-circumferential manner. The channels 104 are in fluidcommunication with four (4) axial distribution channels 106.

With continuing reference to FIG. 11, the axial distribution channels106 extend along the center die member 58 toward the extrusion end 76'.The channels 106 are in fluid communication with a plurality of branchdistribution channels 110, which extend around the center die member 58in a partial circumferential manner, as best shown in FIG. 13. In thepreferred embodiment, the distribution channels 110 are in fluidcommunication with eight (8) axial distribution channels 112 (only fourof which are specifically illustrated in FIG. 11), which also extendalong the member 58 toward the extrusion end 76'. As shown in FIG. 11,the axial distribution channels 112 are in fluid communication with aplurality of generally screw-shaped channels 114 disposed around theextrusion end 76' in a spiral manner.

In operation, extrusion material enters the inlet 72 and travels to thecenter die member 58. At semi-circumferential distribution channel 100,the extrusion material splits and enters the axial distribution channels102. The material travels along the channels 102 and splits again at thebranch distribution channels 104. The extrusion material then enters theaxial distribution channels 106 and travels therealong to the branchdistribution channels 110, where the material splits again and entersthe eight axial distribution channels 112. From the distributionchannels 112, the extrusion material enters the screw-shaped channels114. As with the inner die member, these screw-shaped channels 114therefore function to provide even distribution and good uniformity ofthe extrusion material during the extrusion process.

As shown in FIGS. 4 and 5, extrusion material enters the outer diemember 60 through the inlet 74. Referring now to FIGS. 16 through 20,there are shown various cross-sections of the outer die member 60. Theinlet 74 preferably extends to a trough 120, which is connected to agenerally semi-circumferential distribution channel 122, through whichextrusion material is passed for distribution to the extrusion end 76",as described in greater detail herein below.

With combined reference to FIG. 16 and FIG. 20, the distribution channel122 is preferably in fluid communication with a pair of axialdistribution channels 124 (only one of which is shown in FIG. 16). Asillustrated, the axial distribution channels 124 are preferably disposedsymmetrically around the outer die member 60 and extend therealongtoward the extrusion end 76". In the preferred embodiment, each axialdistribution channel 124 is in fluid communication with a branchdistribution channel 126. As best shown in FIG. 19, the branchdistribution channels 126 extend around the outer die member 60 in agenerally semi-circumferential manner. The branch distribution channels126 are in fluid communication with four (4) axial distribution channels128.

With continuing reference to FIG. 16, the axial distribution channels128 extend along the outer die member 60 toward the extrusion end 76".The channels 128 are in fluid communication with a plurality of branchdistribution channels 130, which extend around the outer die member 60in a partial circumferential manner, as best shown in FIG. 18. In thepreferred embodiment, the distribution channels 130 are in fluidcommunication with eight (8) axial distribution channels 132 (only fourof which are specifically illustrated in FIG. 16), which also extendalong the die member 60 toward the extrusion end 76". As shown in FIG.16, the axial distribution channels 132 are in fluid communication witha plurality of generally screw-shaped channels 134 disposed around theextrusion end 76" in a spiral manner.

In operation, extrusion material enters the inlet 74 and travels to thetrough 120 of the outer die member 60. At semi-circumferentialdistribution channel 122, the extrusion material splits and enters theaxial distribution channels 124. The material travels along the channels124 and splits again at the branch distribution channels 126. Theextrusion material then enters the axial distribution channels 128 andtravels therealong to the branch distribution channels 130, where thematerial splits again and enters the eight axial distribution channels132. From the distribution channels 132, the extrusion material entersthe screw-shaped channels 134. As with the inner and center die members,these screw-shaped channels 134 therefore function to provide gooddistribution and uniformity of the extrusion material during theextrusion process.

FIG. 21 is a cross-section of the crosshead die 36 schematically shownin FIG. 3. Extruder 34 having auger 138 passes material into inlet 140of the die housing 142 which is held together by four axial screws 144and vertical screws 146. The fluoropolymer tube 148 moves in axialfashion through the die housing 142 so that the thermoplastic materialcan be extruded around it resulting in the composite tube 150 exitingfrom the housing. The thermoplastic material passes through inlet 140and moves around channel 152. The desired OD of the thermoplasticmaterial is controlled by die tip 154. The housing is heated by elements156.

The fuel line of the present invention is designed to carry hydrocarbonfuels that are generally used in vehicles such as cars, trucks,airplanes, locomotives, and the like. The fuel is generally heavy inhydrocarbon materials such as propane, butane, aromatics, such asbenzine, toluene and other combustible organic materials. The combinedlaminate or composite therefore prevents the escape of fuel vapors fromthe fuel line. Other fuels such as alcohol-based fuels may also befluids carried in the fuel pipe of the present invention. Further, otherhydrocarbon-based fluids such as hydraulic fluids may likewise beutilized in conjunction with the pipe of the present invention.

It is to be appreciated by using the multiple melt extrusion stages atdifferent positions in the manufacturing process that one canefficiently combine a fluoropolymer that has a high melt extrusiontemperature with a thermoplastic material which has a substantially lessmelt extrusion temperature. By melt extruding the fluoropolymer layersfirst and then cooling down the formed pipe by running the formed tubethrough room temperature water, one can thereafter use a separate anddistinctly different thermoplastic polymer to extrude onto thethermoplastic pipe and avoid thermal degradation of the lower meltingpoint material.

Listed below are description of preferred embodiments where all degreesare degrees Centigrade and all parts are parts by weight, unlessotherwise indicated.

EXAMPLE 1

The surface energy of various treated fluoropolymers was tested. When adyne solution is placed on a material surface and wets out, thatindicates that the material has a higher surface energy than the dynesolution. If the drop "beads up" the material has a lower surface energythan the dyne solution. The use of the dyne solutions is a technique fordetermining the surface energy of materials. Various samples wereprepared of fluoropolymer substrates. Each of the substrates weresubjected to a dyne solution identified as ethyl Cello-Solve-Formamide(Trademark of Corotec of Connecticut, U.S.A.). The sample plaques werewiped clean with a dry cloth to remove surface contamination. Solventwas not used to avoid any surface effects from the residue. The dynesolution was applied in a single side-stroke of the brush to leave a 3/4inch by 1 inch patch of solution. Measurements were taken on bothtreated and untreated samples. The values recorded represent solutionwhich held in a continuous film for greater than 2 seconds. Treatedsamples were prepared by sweeping the discharge head of theEnercon-Dyne-A-Mite device. Treated samples were prepared by sweepingthe discharge head across the plaque at a rate of 1/2 inch to 1/2 inchaway from the sample surface. Two passes were made to ensure completecoverage. Listed below are the test results for the samples tested.

    ______________________________________                                                     initial (E.sub.S -                                                                       After Treatment                                       Sample       Surf. Energy)                                                                            (E.sub.S - Surf. Energy)                              ______________________________________                                        KYNAR 740.sup.1                                                                            42,41,42   44,45,44                                              HYLAR 460.sup.2                                                                            45,46,45   64,58,60                                              HALAR 500.sup.3                                                                            34,35,34   40,37,39                                              ______________________________________                                         .sup.1 KYNAR 740 is a trademark of Atochem of North America for PVDF.         .sup.2 HYLAR 460 is a trademark of Ausimont of Morristown, New Jersey for     PVDF.                                                                         .sup.3 HALAR 500 is a trademark of Ausimont of Morristown, New Jersey for     ECTFE.                                                                   

The results indicate that there is a change in surface energy whichindicates that the Enercon corona discharge device activates thefluorinated samples and that they may be satisfactory substrates forextrusion of a thermoplastic such as a polyamide thereon.

While the forms of the invention herein described constitute presentlypreferred embodiments, many other are possible. It is not intendedherein to mention all the possible equivalent forms or ramifications ofthe invention. It is understood that the terms used herein are merelydescriptive rather than limiting and that various changes may be madewithout departing from the spirit or scope of the invention. Forexample, the invention is equally applicable to a fuel filler neck tubeor to fluoropolymer/thermoplastic composites in general.

What is claimed is:
 1. A method of preparing a fluoropolymer compositecomprising the steps of:(1) chemically activating a formed fluoropolymersubstrate by subjecting the substrate to a charged gaseous atmosphereformed by electrically ionizing a gas which contacts the substrate; and(2) thereafter chemically bonding a layer of a polyamide polymer byapplying said layer of polyamide polymer to the chemically activatedfluoropolymer substrate.
 2. The method of claim 1 wherein thefluoropolymer substrate is an integral multi-layer tube wherein theinner layer is comprised of a conductive fluoropolymer and the outerlayer is of a fluoropolymer resin.
 3. The method of claim 2 wherein theouter layer of the fluoropolymer substrate is activated by subjectingthe outer layer to a corona discharge operating at 250 to 600 joules persecond.
 4. The method of claim 1 wherein the fluoropolymer substrate isa tube.
 5. The method of claim 1 wherein the fluoropolymer substrate ismoving through the charged atmosphere at a rate of 1 to 50 linearfeet/minute.
 6. The method of claim 1 wherein the ionizing takes placeat ambient temperature and pressure.
 7. The method of claim 1 whereinthe ionizing takes place in the presence of ambient pressure andtemperature and ambient atmosphere air.
 8. A method of preparing afluoropolymer composite comprising the steps of:(1) chemicallyactivating a formed fluoropolymer substrate by subjecting the substrateto a charged gaseous atmosphere formed by electrically ionizing a gaswhich contacts the substrate, wherein the fluoropolymer substrate is anintegral multi-layer tube, wherein the inner layer is comprised of aconductive fluoropolymer and the outer layer is of a fluoropolymerresin; and (2) thereafter chemically bonding a layer of polyamidepolymer by applying said layer of polyamide polymer to the chemicallyactivated fluoropolymer substrate.